1. Field of Invention
The present invention relates to a micro-electro-mechanical system (MEMS) technology with semiconductor fabrication technology. More particularly, the present invention relates to a method for fabricating a MEMS device.
2. Description of Related Art
MEMS devices have been widely fabricated using semiconductor fabricating process. However, it is still not easy to be integrated into the standard MOS (metal-oxide semiconductor) process, such as complementary MOS (CMOS) device. In general, a discrete MEMS device and a CMOS ASIC chip are packaged to a single die for application. However, the cost and performance for current technology cause not being popular. It is intended to develop a CMOS MEMS technology, so that the process for fabricating the MEMS can be compatible with the process for fabricating the CMOS device.
MEMS Condenser Device consists of a stiff Backplate and a compliant diaphragm. Conventional the diaphragm is constructed by thin film material and clamped by a surrounding frame. The temperature expansion coefficient and crystal mismatch of the diaphragm material and supporting frame will cause to residual stress existing in the diaphragm. The unrelieved residual stress in the diaphragm will deteriorate the diaphragm compliant.
FIG. 1 is a cross-sectional view, schematically illustrating a conventional structure of MEMS microphone. In FIG. 1, the MEMS microphone includes a substrate 100, such as the silicon substrate. A hard mask layer 101, such as nitride, oxide or metal layer, is optionally formed on the substrate at a backside. The substrate 100 has a cavity 102 and the venting holes 106. A portion 104b of the substrate 100 above the cavity 102 may have the doped layer 104a on the portion 104b of the substrate 100. A structural dielectric layer 108 is formed on the substrate 100. The structural dielectric layer 108 has the dielectric layer and the conductive structure embedded in the dielectric layer. A diaphragm 112 is formed above the substrate 100 in corresponding to the cavity 102. The diaphragm 112 is clamped into the structural dielectric layer 108 at the region 114. As a result, a chamber 110 is formed in connection with the cavity by the venting holes 106. As mentioned above, the diaphragm 112 is clamped in the structural dielectric layer 108 without moving. This cause the poor sensitivity, for example.